Dry Rolling Contact Research Articles

Consideration of Power Transmission Characteristics in a Micro-Gear Train.

Characteristics related to power transmission in the micro-domain, based on dry rolling contact of the gears, were investigated using a 3D-printed gear train with a pitch circle diameter of 84 µm in order to experimentally compare the power transmission efficiency in the macro- and micro-domains. For a basic gear train with two intermeshing gears, it was shown that the gear train in the micro-domain was capable of transmitting power to the same extent as in the macro-domain. However, in gear trains with complex power transmission paths, assuming a planetary gear train with multiple meshing gears, it has been shown that the power transmission characteristics of micro-domain gears differ from those in the macro-domain. The use of gear trains in the micro-region necessitates consideration of the loss of transmitted torque due to contact between tooth surfaces, which is unique to the micro-region and different from its use in the macro-region.

Wear Failure of PEEK-Alumina Ball Bearings in Dry Rolling Contact at 600 rpm - Part 2: Observation of Wear on Retainer

In our previous paper[6], the effects of the retainer wear failure on the friction torque were investigated. In the present paper, to research the failure of the retainers of the PEEK-alumina ball bearings tested under dry rolling contact, the upper and bottom surfaces and the sections of the retainer pockets were observed. The wear damage was found on the surface of the upper and bottom surfaces. On the sections of the pocket, the changes due to wear at the pocket edge was found. On the worn curves of the sections, large scatter of the curvature center positions were numerically calculated in both specimens. The balls moved relatively for the retainer unit to the upper or bottom sides. These results indicate that the wear changed the pocket shape, and the ball could not become to keep the position for the retainer unit. The wear of the pocket caused the failure of the retainer.

Wear Failure of PEEK-Alumina Ball Bearings in Dry Rolling Contact at 600 rpm - Part 1: Effect of Failure due to Wear Damage on Friction Torque

The rolling contact fatigue of PEEK-alumina ball bearings in non-lubrication was tested under 500 N and 600 N. During the tests, the friction torque was measured. The retainers under both conditions broke during the tests, and rubbed on the upper and bottom races. The friction features were not different between 500 N and 600 N. However, the black colored surfaces on the races and retainer were identified only in the test under 600 N. The wear loss of the bearing tested under 600 N was larger than that under 500 N. From these results, the specimen under 600 N received the heavier wear damages than that under 500 N, and the worn surface was not related to the friction torque. The wear damages of the inner elements and the outer rings in the retainer were larger than those of the races and 9-alumina balls in both specimens.

無潤滑環境下におけるPEEK-PPSハイブリッド軸受の摩耗量に及ぼす回転速度と荷重の関係

無潤滑環境下におけるPEEK-PPSハイブリッド軸受の摩耗量に及ぼす回転速度と荷重の関係

1207 UHMWPEスラスト軸受の大気中における溝形状が摩耗に与える影響(OS8-5 材料力学と計算力学の新展開)

1207 UHMWPEスラスト軸受の大気中における溝形状が摩耗に与える影響(OS8-5 材料力学と計算力学の新展開)

Wear of hybrid radial bearings (PEEK ring-PTFE retainer and alumina balls) under dry rolling contact

Wear of poly ether-ether-ketone (PEEK) radial ball bearing (composed of PEEK ring, PTFE composite retainer and alumina balls) was investigated. The PEEK radial bearings were produced by lathe machining, and their rolling contact wear tests were carried out at high rotational speed in dry condition. The PEEK adhesion film including PTFE and graphite wear particles was observed on the raceway of the bearing׳s inner ring during the test. Due to the PEEK–PTFE adhesion film accumulation, the wear rate decreased to one tenth of all-PEEK bearing. Moreover alumina balls were not stuck, and the operation temperature was less than glass transition temperature of PEEK. It was found that the PEEK–PTFE adhesion film improved dramatically wear and rotational performance of the bearing.

Relationship between Life, Load and Rotation Speed of UHMWPE Bearing under Dry Rolling Contact Fatigue

The polymer bearings have been widely used in recent years. In this study, ultra-high-molecular-weight-polyethylene (UHMWPE) is investigated. In order to investigate the relation between the lives, loads and rotation speeds, rolling contact fatigue tests were conducted. It was found that rotation speed related to the bearing life and wear loss.

Relationship between Load, Rotation Speed and, Strength in All - PEEK and PEEK Race – PTFE Retainer Hybrid Polymer Bearings under Dry Rolling Contact Fatigue

The production of bearings is focusing on polymers, such as polyether ether ketone (PEEK), a tough semi-crystalline thermoplastic polymer with excellent mechanical properties and polytetrafluoroethylene (PTFE), a material with low friction coefficient. The purpose of this study was to establish the properties of hybrid PEEK races – PTFE retainer bearings. Rolling contact fatigue tests were performed in order to investigate the wear properties of such components and the relation between load and rotation speed. It is concluded that by using a PTFE retainer, no wear occurs under thrust load ranging from 200N to 800N at 300rpm.

Influence of a single axisymmetric asperity on surface stresses during dry rolling contact

The effect from contact loading of some single axisymmetric asperities as a potential mechanism for surface initiated rolling contact fatigue was investigated numerically using FEM. Computational results were compared to properties of some rolling contact fatigue craters, or spalls, in the teeth surfaces of four driving gear wheels. The gears were geometrically identical but had experienced slightly varying load conditions. The residual surface stresses of a used teeth with spalls were measured using the hole drilling technique. The combined cylinder asperity contact was first modelled with a stationary model in which an asperity was introduced at the contact rim. By varying asperity height, width, position and contact load dangerous asperity configurations were sought for. The gear contact close to the rolling circle was modelled as two rolling cylinders. A single asperity was introduced into the contact surface of one of them. Due to the presence of the asperity a three-dimensional contact model was required. The simulation included residual stresses from heat treatment and plastic deformation due to the first roll cycle. Thus, the stress results were computed from the second roll cycle. The important overall conclusion was that a single asperity may serve as a stress raiser in the contact surfaces. Furthermore, the computed values of the increased surface stresses were comparable to those that are reported in the literature to give cracks. Example of dangerous asperity dimensions were noted and changes in residual stresses from moderate plastic deformation during rolling were estimated. The asperity deformed plastically during over-roll but remained sufficiently high. The trajectory of the largest principal stress was computed, starting from the position in front of a loaded asperity with maximum tensile stress. The trajectory was compared to the spalling entry angle of a representative spall. For some asperity-cylinder configurations a convex region with large stress was found in the surface. The presence of such a convex stress region was compared to the convex shaped of the spalling tip that sometimes could be found.

A New Method for the Evaluation of Wear Damage in Dry Rolling Contact by Sound Intensity Level and Residual Stress Measurements

The contact fatigue wear of rolling surfaces is associated with the behavior of dislocations located at the specimen surface and subsurface. This behavior depends on the Hertzian Pressure and specimen shear strength, which affect the residual stress fields developed during cyclic loading. This work describes a new nondestructive method to evaluate changes on the residual stress fields and wear damage in dry rolling contact. A disc-disc testing machine was used into a semi-anechoic chamber to evaluate the audible sound signal (noise intensity level) continuously generated by the mechanical contact. Pairs of discs of heat treated DIN 100Cr6 (AISI 52100) steel were tested under Hertzian nominal pressures from P o = 1.5 GPa to P o = 2.5 GPa, at velocities of 40±0.5 m/s. The sound signals were later distributed into box-and-plot graphics which indicated four percentile groups (quartiles) and revealed the main tendency and dispersion of these signals. An XRD analysis, using the sin 2 ψ technique was applied to measure the residual stresses and to associate them with the noise intensity level quartiles at different stages of testing. Microstructural analyses of tested disc surfaces and resulting debris, using a Scanning Electron Microscope (SEM), showed a relation between the different noise levels and surface damage mechanisms, such as microspalling, micropitting, plastic deformation, delamination and brittle fracture.

Investigation of rolling resistance and surface damage of rolling elements

It has been well established that resistant force and wear that occur during rolling motion depend on several factors such as material type, hardness, subsurface microstructure, applied load, and speed. The purpose of this work is to investigate the effect of microstructure and the state of deformed layer on the rolling contact characteristics in dry and lubricated rolling contacts. The results of this work show that the rolling resistance behavior depends on the state of the deformed layer. Also, lubrication can reduce the plastic flow at the surface but may still have an effect on the subsurface strain. The cross-sectional view of the microstructure shows that surface traction has a difinite effect on the morphology of the surface region. That is, significant slip seems to have taken place between the ball than those of the dry rolling case. The surface generation effects were significantly less compared to the case of dry rolling contact.

Dry rolling wear of different materials induced by a non-uniform hertzian pressure distribution

This paper reports the tribological correlation between the wear behaviour in dry rolling contact with a non-uniform hertzian pressure distribution and the material properties of SAE52100 steel, silicon nitride ceramic (Si 3N 4) and amorphous metal carbides containing a hydrogenated carbon coating (WC/C). For this examination, a new wear rig was designed as an attachment to a standard Amsler two-roller machine, in which the contact mechanism of any cam/cam follower system can be simulated. The tests were carried out with different contact pairs. The wear behaviour was observed in situ and the mechanisms of damage were examined by optical and electron microscopy as well as laser profiling. Moreover, the changes in different tribological parameters were observed. The results show that the failure mechanism of steel is dominated by adhesion and tribo-oxidation. The ceramic fails typically by microcracking and the failure of WC/C is mostly attributed to mild abrasion followed by adhesion of the substrate steels. Steel vs. steel rollers fail after less than 800 contact cycles, Si 3N 4 vs. steel after 1090 contact cycles, Si 3N 4 vs. Si 3N 4 after 1646 contact cycles, WC/C vs. steel after 145 775 contact cycles and WC/C vs. WC/C after more than 1 million contact cycles. These values are discussed in the light of other microstructural and characterization results.

Dry rolling wear of different materials induced by a non-uniform hertzian pressure distribution

This paper reports the tribological correlation between the wear behaviour in dry rolling contact with a non-uniform hertzian pressure distribution and the material properties of SAE52100 steel, silicon nitride ceramic (Si3N4) and amorphous metal carbides containing a hydrogenated carbon coating (WC/C). For this examination, a new wear rig was designed as an attachment to a standard Amsler two-roller machine, in which the contact mechanism of any cam/cam follower system can be simulated. The tests were carried out with different contact pairs. The wear behaviour was observed in situ and the mechanisms of damage were examined by optical and electron microscopy as well as laser profiling. Moreover, the changes in different tribological parameters were observed. The results show that the failure mechanism of steel is dominated by adhesion and tribo-oxidation. The ceramic fails typically by microcracking and the failure of WC/C is mostly attributed to mild abrasion followed by adhesion of the substrate steels. Steel vs. steel rollers fail after less than 800 contact cycles, Si3N4 vs. steel after 1090 contact cycles, Si3N4 vs. Si3N4 after 1646 contact cycles, WC/C vs. steel after 145 775 contact cycles and WC/C vs. WC/C after more than 1 million contact cycles. These values are discussed in the light of other microstructural and characterization results.

Rolling wear of tin coatings induced by non-uniform hertzian stress distribution

The wear of TiN coatings in dry rolling contact with a non-uniform Hertzian stress distribution has been studied. Wear behaviour was observed in situ and the mechanisms of damage were examined by optical and electron microscopy and laser profiling. Changes of friction coefficient, weight, residual stress, percentage of undamaged TiN, and surface roughness were also observed. The failure mechanism of TiN coated SAE 52100 steel running against steel rollers was dominated by microcracking, transfer of material, and fatigue; that of TiN against TiN (both on M2 tool steel substrates) was principally adhesive failure, which occurred at the near surface carbides in the steel. Tests involving TiN coated rollers running against TiN coated rollers lasted 39 800 rolling contact cycles, whereas TiN versus steel failed after 8600 cycles and steel versus steel after less than 1700 cycles.

The role of oxidation in the wear of plasma nitrided and PVD TiN coated steel

The wear behaviour of plasma nitrided En40B steel has been investigated under dry rolling contact with applied sliding traction. Particular attention has been paid to the examination of the tribochemical reaction, i.e. oxidation, of the nitrided surface during the wear process. X-ray diffraction, optical and scanning electron microscopes have been employed to study the wear debris, worn surfaces and subsurfaces. Experiments revealed that, as a result of the hardening effect induced by plasma nitriding, wear of the nitrided steel occurred in a mild mode via oxidation of the contact surfaces and the subsequent removal of the oxide products, and the overall wear rate was dominated by the rate of oxidation of the contact surfaces. However, the unnitrided steel was worn via surface and subsurface shear deformation, leading to severe wear. In order to further improve the wear resistance of the steel, a thin, hard titanium nitride (TiN) coating was deposited on top of the nitrided steel by ion plating. Such duplex treated steel possessed superior resistance to both subsurface shear deformation and tribo-oxidation, thus ensuring minimisation of the wear rate.

Load Bearing Capacity of Plasma Nitrided Steelunder Rolling–Sliding Contact

The wear behaviour of plasma nitrided low alloy steel has been investigated under dry rolling contact with sliding traction. Particular attention was paid to subsurface shear behaviour during the wear process, and to prediction of the load bearing capacity of the nitrided specimens. A simple model has been developed to describe the influence of hardened depth, strength and residual stresses of the nitrided case, and coefficient of friction on the initiation of shear deformation in the contact bodies during the wear process. Experimental results and the model show that a relatively thick and strong nitrided case is required for the specimens to bear high loads without severe wear. The model also indicates the complex effect of compressive residual stresses on the maximum shear stress distribution in the subsurface induced by the applied forces.

Wear Mechanism of Ceramic Materials in Dry Rolling Friction

Wear tests in dry rolling contact were carried out at room temperature on five ceramic materials, such as silicon nitride, silicon carbide, cermet, titania, and alumina. The results showed that wear rate of silicon nitride was smaller than any of the other ceramic materials and bearing steel. Observations of worn surface and wear debris revealed that ceramic materials have two types of wear, one related to real contact area and another related to Hertzian contact area. It was also found that brittle fracture dominates the wear process of ceramic materials in dry rolling contact. Based on the experimental results, wear rate of ceramic materials was expressed with a new nondimensional parameter.

Wear properties of silicon nitride in rolling contact

The wear properties of silicon nitride were examined in dry rolling contact. The wear coefficient of silicon nitride in pure rolling was of the order of 10 −6 at the initial stage of wear and of the order of 10 −8 at the steady stage of wear under hertzian pressures of 1.06, 1.30, 1.50 and 1.83 GPa. The wear coefficient of silicon nitride in rolling-sliding was of the order of 10 −3 under hertzian pressures of 1.06, 1.50 and 1.83 GPa. The original grinding marks were decreased by the initial wear. Then a very smooth surface appeared in the steady state and its centre-line average roughness R a was 0.02 μm. In contrast, pitting and the adhesive accumulation of thin film debris on the surface started to occur in the steady stage of wear. Three typical types of wear debris were distinguished. One of these, which was a glassy film, was confirmed to have an SiO 2 structure.

Creep and Wear Due to Microslip in Conforming Rolling Contacts

The paper presents experimental results for the creep and wear due to microslip under dry rolling contact conditions. Creep results show good correlation with the strip theory predictions for conforming geometric contacts. The wear effects of increasing the tangential traction on plane rolling contacts are explained using an incremental wear law related to the square of both the local pressure and the local slip velocity. Various degrees of geometric conformity are examined and support the theoretical arguments for the minimum wear conditions associated with any particular loading in terms of a prescribed geometric conformity.

A review of the theory of rolling contact stresses

Recent developments in the theory of rolling contact stresses are reviewed. They follow three main lines: 1. (1) elastic stresses due to slip and friction at the contact interface, 2. (2) pressures developed in elasto-hydrodynamic lubricating films and 3. (3) the influence of inelastic (visco-elastic or plastic) behaviour of the material of the rolling solids. The theory of dry rolling contact of elastic solids is now at an advanced state of development. Studies of lubricated rolling and inelastic deformation are restricted to the two-dimensional problems of rolling cylinders. It has been possible however to put forward a tentative theoretical load-carrying capacity for lubricated metal rollers, above which continuous permanent deformation will take place. It is suggested that the strength of actual rolling surfaces falls below the theoretical limit due to non-homogeneity of the material and the roughness of the surfaces. These effects are at present beyond the scope of theory but would well repay study.